1. Field of the invention
The present invention relates to an organic electroluminescent display device, and is particularly suitable for an organic electroluminescent display device in which extended lifetime and improved reliability are achieved by preventing reduction in luminous efficiency due to a plasticizer trapped in an organic electroluminescent element during a manufacturing process of the same.
2. Description of Related Art
As a flat panel display device, a liquid crystal display device (LCD), a plasma display device (PDP), a field emission display device (FED), an organic electroluminescent display device (hereinafter also referred to as an OLED element) and the like are in practical use or under development for practical use. Among them, the organic electroluminescent display device representing a thin, lightweight emissive display device is a particularly promising future display device.
The organic electroluminescent display device is classified into so-called bottom emission and top emission types. In the bottom emission type organic electroluminescent display device, an organic electroluminescent element has a light emitting structure in which a transparent electrode (such as ITO) as a first electrode or one electrode, an organic multilayer film that emits light by application of an electric field (also referred to as an organic light emitting layer), and a reflective metal electrode as a second electrode or the other electrode are sequentially stacked on an insulating substrate, preferably a glass substrate. A plurality of the organic electroluminescent elements are arranged in a matrix and their stacked structures are covered by another substrate referred to as an encapsulation can in order to separate the light emitting structure from outer atmosphere. For example, the transparent and metal electrodes are used as an anode and a cathode, respectively, and an electric field is applied across these electrodes to inject carriers (electrons and holes) into the organic multilayer film, resulting in light emission from the organic multilayer film. The emitted light exits through the glass substrate to the outside.
On the other hand, the top emission type organic electroluminescent display device uses a reflective metal electrode as the above-mentioned one electrode and a transparent electrode, such as ITO, as the other electrode, applies an electric field across these electrodes to cause the organic multilayer film to emit light, and outputs the emitted light through the above-mentioned other electrode. The top emission type uses a transparent substrate (an encapsulation substrate), preferably a glass plate, as the encapsulation can in the bottom emission type.
The principle of how the organic electroluminescent element (hereinafter also referred to as the OLED element) emits light is as follows: That is, electrons, which is one carrier, from the cathode and holes, which is the other carrier, from the anode are injected to the multilayer film containing an organic fluorescent material. When the carriers are recombined in the organic layer, excitons are produced. When the excitons return to the ground state, they emit light.
The OLED element is typically formed of multiple organic layers stacked on a substrate. Typically, the OLED element is often formed of four organic layers including a hole injection layer, a hole transport layer, an emitting layer and an electron transport layer, or five organic layers further including an electron injection layer on the electron transport layer. Related art of this type is disclosed, for example, in JP-A-5-258859, JP-A-5-258860 and JP-A-5-275172.